Method for managing network failures

ABSTRACT

A disclosure according to the present specification provides a method of having an access by a terminal subscribing to a first public land mobile network (PLMN). The method may comprise a step of transmitting a first request message to a network node via a base station. The base station may be a base station of a second PLMN that broadcasts system information including information about the first PLMN. The method may comprise a step of receiving, from the network node, a first response message that is a response to the first request message. The first response message may include information indicating that there is a service failure in the first PLMN. The method may comprise a step of transmitting a second request message to the second PLMN or reselecting another PLMN instead of the first PLMN, which has a service failure, on the basis of the first response message including the information.

TECHNICAL FIELD

The present specification relates to mobile communication.

BACKGROUND

System Architecture Evolution (SAE) that has been performed based on 3rd Generation Partnership Project (3GPP) Service and System Aspects (SA) Working Group 2 (WG2) is research regarding network technology that aims to determine the structure of a network and to support mobility between heterogeneous networks in line with an LTE task of a 3GPP Technical Specification Group (TSG) Radio Access Network (RAN) and is one of recent important standardization issues of 3GPP. SAE is a task for developing a 3GPP system into a system that supports various radio access technologies based on an Internet Protocol (IP), and the task has been carried out for the purpose of an optimized packet-based system which minimizes transmission delay with a more improved data transmission capability.

An Evolved Packet System (EPS) higher level reference model defined in 3GPP SA WG2 includes a non-roaming case and roaming cases having various scenarios, and for details therefor, reference can be made to 3GPP standard documents TS 23.401 and TS 23.402. A network configuration of FIG. 1 has been briefly reconfigured from the EPS higher level reference model.

FIG. 1 shows a structure of an evolved mobile communication network.

An Evolved Packet Core (EPC) may include various elements. FIG. 1 illustrates a Serving Gateway (S-GW) 52, a Packet Data Network Gateway (PDN GW) 53, a Mobility Management Entity (MME) 51, a Serving General Packet Radio Service (GPRS) Supporting Node (SGSN), and an enhanced Packet Data Gateway (ePDG) that correspond to some of the various elements.

The S-GW 52 is an element that operates at a boundary point between a Radio Access Network (RAN) and a core network and has a function of maintaining a data path between an eNodeB 22 and the PDN GW 53. Furthermore, if a terminal (or User Equipment (UE)) moves in a region in which service is provided by the eNodeB 22, the S-GW 52 plays a role of a local mobility anchor point. That is, for mobility within an E-UTRAN (Evolved Universal Mobile Telecommunications System (Evolved-UMTS) Terrestrial Radio Access Network defined after 3GPP release-8), packets can be routed through the S-GW 52. Furthermore, the S-GW 52 may play a role of an anchor point for mobility with another 3GPP network (i.e., a RAN defined prior to 3GPP release-8, for example, a UTRAN or Global System for Mobile communication (GSM)/Enhanced Data rates for Global Evolution (EDGE) Radio Access Network (GERAN)).

The PDN GW (or P-GW) 53 corresponds to the termination point of a data interface toward a packet data network. The PDN GW 53 can support policy enforcement features, packet filtering, charging support, etc. Furthermore, the PDN GW (or P-GW) 53 can play a role of an anchor point for mobility management with a 3GPP network and a non-3GPP network (e.g., an untrusted network, such as an Interworking Wireless Local Area Network (I-WLAN), a trusted network, such as a Code Division Multiple Access (CDMA)).

In the network configuration of FIG. 1 , the S-GW 52 and the PDN GW 53 have been illustrated as being separate gateways, but the two gateways may be implemented in accordance with a single gateway configuration option.

The MME 51 is an element for performing the access of a UE to a network connection and signaling and control functions for supporting the allocation, tracking, paging, roaming, handover, etc. of network resources. The MME 51 controls control plane functions related to subscribers and session management. The MME 51 manages numerous eNodeBs 22 and performs conventional signaling for selecting a gateway for handover to another 2G/3G networks. Furthermore, the MME 51 performs functions, such as security procedures, terminal-to-network session handling, and idle terminal location management.

The SGSN handles all packet data, such as a user's mobility management and authentication for different access 3GPP networks (e.g., a GPRS network and an UTRAN/GERAN).

The ePDG plays a role of a security node for an unreliable non-3GPP network (e.g., an I-WLAN and a Wi-Fi hotspot).

As described with reference to FIG. 1 , a terminal (or UE) having an IP capability can access an IP service network (e.g., IMS), provided by a service provider (i.e., an operator), via various elements within an EPC based on non-3GPP access as well as based on 3GPP access.

Furthermore, FIG. 1 shows various reference points (e.g., S1-U and S1-MME). In a 3GPP system, a conceptual link that connects two functions that are present in the different function entities of an E-UTRAN and an EPC is called a reference point. Table 1 below defines reference points shown in FIG. 1 . In addition to the reference points shown in the example of Table 1, various reference points may be present depending on a network configuration.

TABLE 1 REFERENCE POINT DESCRIPTION S1-MME A reference point for a control plane protocol between the E-UTRAN and the MME S1-U A reference point between the E-UTRAN and the S-GW for path switching between eNodeBs during handover and user plane tunneling per bearer S3 A reference point between the MME and the SGSN that provides the exchange of pieces of user and bearer information for mobility between 3GPP access networks in idle and/or activation state. This reference point can be used intra-PLMN or inter-PLMN (e.g. in the case of Inter- PLMN HO). S4 A reference point between the SGW and the SGSN that provides related control and mobility support between the 3GPP anchor functions of a GPRS core and the S-GW. Furthermore, if a direct tunnel is not established, the reference point provides user plane tunneling. S5 A reference point that provides user plane tunneling and tunnel management between the S-GW and the PDN GW. The reference point is used for S-GW relocation due to UE mobility and if the S-GW needs to connect to a non-collocated PDN GW for required PDN connectivity S11 A reference point between the MME and the S-GW SGi A reference point between the PDN GW and the PDN. The PDN may be a public or private PDN external to an operator or may be an intra- operator PDN, e.g., for the providing of IMS services. This reference point corresponds to Gi for 3GPP access.

Among the reference points shown in FIG. 1 , S2 a and S2 b correspond to non-3GPP interfaces. S2 a is a reference point that provides related control and mobility support between trusted non-3GPP access and PDN GWs to the user plane. S2 b is a reference point that provides related control and mobility support between ePDG and P-GW to the user plane. FIG. 2 is an exemplary diagram showing the general functions of the main nodes of the E-UTRAN and the EPC.

As shown, the eNodeB 20 may perform functions for routing to a gateway while the RRC connection is active, scheduling and transmission of paging messages, scheduling and transmission of a Broadcast Channel (BCH), dynamic allocation of resources in uplink and downlink to the UE, configuration and provision for measurement of the eNodeB 20, radio bearer control, radio admission control, and connection mobility control, etc. Within the EPC, the eNodeB 20 may perform paging generation, LTE_IDLE state management, user plane encryption, EPS bearer control, encryption and integrity protection of NAS signaling.

FIG. 3 is an exemplary diagram showing the structure of a radio interface protocol in the control plane between the UE and the eNodeB. FIG. 4 is another exemplary diagram showing the structure of a radio interface protocol in the user plane between the UE and the eNB.

The radio interface protocol is based on the 3GPP radio access network standard. The radio interface protocol horizontally consists of a physical layer, a data link layer, and a network layer. The radio interface protocol is vertically divided into a user plane for transmitting data information and a control plane for transmitting a control signal.

The protocol layers may be divided into L1 (Layer 1), L2 (Layer 2), and L3 (Layer 3) based on the lower three layers of the Open System Interconnection (OSI) standard model widely known in communication systems.

Hereinafter, each layer of the radio protocol in the control plane shown in FIG. 3 and the radio protocol in the user plane shown in FIG. 4 will be described.

The first layer, the physical layer, provides an information transfer service using a physical channel. The physical layer is connected to an upper Medium Access Control (MAC) layer through a transport channel, and data between the MAC layer and the physical layer is transmitted through the transport channel. And, data is transferred between different physical layers, that is, between the physical layers of the transmitting side and the receiving side through a physical channel

A physical channel consists of several subframes on the time axis and several sub-carriers on the frequency axis. Here, one sub-frame is composed of a plurality of symbols on the time axis and a plurality of sub-carriers. One subframe is composed of a plurality of resource blocks, and one resource block is composed of a plurality of symbols and a plurality of subcarriers. A Transmission Time Interval (TTI), which is a unit time for data transmission, is 1 ms corresponding to one subframe.

According to 3GPP LTE, the physical channels existing in the physical layers of the transmitting side and the receiving side may be divided into a data channel, i.e., Physical Downlink Shared Channel (PDSCH) and a Physical Uplink Shared Channel (PUSCH), and a control channel, i.e., a Physical Downlink Control Channel (PDCCH), a Physical Control Format Indicator Channel (PCFICH), a Physical Hybrid-ARQ Indicator Channel (PHICH), and a Physical Uplink Control Channel (PUCCH).

The PCFICH transmitted in the first OFDM symbol of the subframe carries a Control Format Indicator (CFI) regarding the number of OFDM symbols used for transmission of control channels in the subframe (i.e., the size of the control region). The wireless device first receives the CFI on the PCFICH and then monitors the PDCCH.

Unlike the PDCCH, the PCFICH does not use blind decoding and is transmitted through a fixed PCFICH resource of a subframe.

The PHICH carries a Positive-Acknowledgement (ACK)/Negative-Acknowledgement (NACK) signal for a UL Hybrid Automatic Repeat Request (HARQ). An ACK/NACK signal for uplink (UL) data on a PUSCH transmitted by a wireless device is transmitted on a PHICH.

A Physical Broadcast Channel (PBCH) is transmitted in the first four OFDM symbols of the second slot of the first subframe of the radio frame. The PBCH carries system information essential for a wireless device to communicate with a base station, and the system information transmitted through the PBCH is called a Master Information Block (MIB). In comparison, the system information transmitted on the PDSCH indicated by the PDCCH is referred to as a System Information Block (SIB).

PDCCH may carry resource allocation and transmission format of a Downlink Shared Channel (DL-SCH), resource allocation information of an Uplink Shared Channel (UL-SCH), paging information on the PCH, system information on the DL-SCH, resource allocation of a higher layer control message such as a random access response transmitted on the PDSCH, a set of transmission power control commands for individual UEs in an arbitrary UE group, and activation of Voice over Internet Protocol (VoIP). A plurality of PDCCHs may be transmitted in the control region, and the UE may monitor the plurality of PDCCHs. The PDCCH is transmitted on an aggregation of one or several consecutive Control Channel Elements (CCEs). The CCE is a logical allocation unit used to provide the PDCCH with a coding rate according to the state of a radio channel. The CCE corresponds to a plurality of resource element groups. The format of the PDCCH and the possible number of bits of the PDCCH are determined according to the correlation between the number of CCEs and the coding rates provided by the CCEs.

Control information transmitted through the PDCCH is referred to as Downlink Control Information (DCI). DCI may include PDSCH resource allocation (this may also be called a DL grant), PUSCH resource allocation (this may also be called an UL grant), a set of transmit power control commands for individual UEs in an arbitrary UE group and/or activation of Voice over Internet Protocol (VoIP).

In the second layer, there are several layers. First, the MAC layer plays a role in mapping various logical channels to various transport channels, and plays a role in logical channel multiplexing that maps multiple logical channels to one transport channel The MAC layer is connected to the Radio Link Control (RLC) layer, which is the upper layer, by a logical channel Logical channels are largely divided into a control channel for transmitting control plane information and a traffic channel for transmitting user plane information according to the type of information to be transmitted.

The RLC layer of the second layer plays a role in diving and concatenating the data received from the upper layer to adjust the data size so that the lower layer is suitable for data transmission in the radio section. In addition, in order to ensure the various Quality of Service (QoS) required by each Radio Bearer (RB), three operation modes, i.e., Transparent Mode (TM), Un-acknowledged Mode (UM, no response mode), and Acknowledged Mode (AM, response mode), are provided. In particular, AM RLC performs a retransmission function through an Automatic Repeat and Request (ARQ) function for reliable data transmission.

The Packet Data Convergence Protocol (PDCP) layer of the second layer plays a role in header compression to reduce the size of the IP packet header which is relatively large and contains unnecessary control information in order to efficiently transmit IP packets such as IPv4 or IPv6 in a radio section with a small bandwidth. This serves to increase the transmission efficiency of the radio section by transmitting only necessary information in the header part of the data. In addition, in the LTE system, the PDCP layer also performs a security function, which consists of ciphering to prevent data interception by a third party and integrity protection to prevent data manipulation by a third party.

The Radio Resource Control (RRC) layer located at the top of the third layer is defined only in the control plane, and are responsible for the control of logical channels, transport channels and physical channels related to the configuration, reconfiguration, and release of the RB. In this case, the RB means a service provided by the second layer for data transfer between the UE and the E-UTRAN.

If there is an RRC connection between the RRC of the UE and the RRC layer of the wireless network, the UE is in the RRC connected mode, otherwise it is in the RRC idle mode.

Hereinafter, an RRC state of the UE and an RRC connection method will be described. The RRC state refers to whether or not the RRC of the UE is logically connected to the RRC of the E-UTRAN. If it is connected, it is called an RRC_CONNECTED state, and if it is not connected, it is called an RRC_IDLE state. Since the UE in the RRC_CONNECTED state has an RRC connection, the E-UTRAN can determine the existence of the UE on per cell, and thus can effectively control the UE. On the other hand, the E-UTRAN cannot detect the existence of the UE in the RRC_IDLE state, and the core network manages the UE per Tracking Area (TA), which is larger regional unit than the cell. That is, the UE in the RRC_IDLE state is only checked whether the UE exists in a larger area than the cell, and in order to receive a normal mobile communication service such as voice or data, the UE should transit to the RRC_CONNECTED state. Each TA is identified through a Tracking Area Identity (TAI). The UE may configure the TAI through a Tracking Area Code (TAC), which is information broadcast in a cell.

When the user turns on the UE for the first time, the UE first searches for an appropriate cell, then establishes an RRC connection in the corresponding cell, and registers information on the UE in the core network. After this, the UE stays in the RRC_IDLE state. The UE staying in the RRC_IDLE state (re)selects a cell as needed, and looks at system information or paging information. This is called camping on the cell. The UE, which stayed in the RRC_IDLE state, establishes an RRC connection with the RRC of the E-UTRAN through an RRC connection procedure and then transits to the RRC_CONNECTED state only when it is necessary to establish an RRC connection. There are several cases in which the UE in the RRC_IDLE state needs to establish an RRC connection, e.g., when uplink data transmission is required for reasons such as a user's call attempt, or when a paging message is received from E-UTRAN, for transmission of a response message to the paging message.

The Non-Access Stratum (NAS) layer located above the RRC layer performs functions such as session management and mobility management.

Hereinafter, the NAS layer shown in FIG. 3 will be described in detail.

Evolved Session Management (ESM) belonging to the NAS layer performs functions such as default bearer management and dedicated bearer management, and is responsible for controlling the UE to use the Packet Switched (PS) service from the network. The default bearer resource has the characteristic that it is allocated from the network when it is connected to a specific PDN for the first time. At this time, the network allocates an IP address usable by the UE so that the UE can use the data service, and also allocates QoS of the default bearer. LTE supports two types: a bearer with a Guaranteed Bit Rate (GBR) QoS characteristic that guarantees a specific bandwidth for data transmission and reception, and a non-GBR-bearer with a best effort QoS characteristic without a bandwidth guarantee. do. In the case of a default bearer, a non-GBR-bearer is allocated. In the case of a dedicated bearer, a bearer having QoS characteristics of GBR or non-GBR may be allocated.

The bearer allocated to the UE by the network is called an EPS bearer, and when the EPS bearer is allocated, the network allocates one ID. This is called the EPS bearer ID. One EPS bearer has QoS characteristics of Maximum Bit Rate (MBR) and Guaranteed Bit Rate (GBR) or Aggregated Maximum Bit Rate (AMBR).

FIG. 5 a is a flowchart illustrating a random access procedure in 3GPP LTE.

The random access procedure is used for the UE 10 to obtain UL synchronization with the base station, i.e., the eNodeB 20, or to be allocated UL radio resources.

The UE 10 receives a root index and a Physical Random Access Channel (PRACH) configuration index from the eNodeB 20. There are 64 candidate random access preambles defined by a Zadoff-Chu (ZC) sequence for each cell, and the root index is a logical index for the UE to generate 64 candidate random access preambles.

Transmission of the random access preamble is limited to specific time and frequency resources for each cell. The PRACH configuration index indicates a specific subframe and preamble format in which the random access preamble can be transmitted.

The UE 10 transmits a randomly selected random access preamble to the eNodeB 20. The UE 10 selects one of 64 candidate random access preambles. Then, the UE 10 selects a corresponding subframe according to the PRACH configuration index. The UE 10 transmits the selected random access preamble in the selected subframe.

Upon receiving the random access preamble, the eNodeB 20 transmits a Random Access Response (RAR) to the UE 10. The random access response is detected in two steps. First, the UE 10 detects a PDCCH masked with a Random Access Radio Network Temporary Identity (RA-RNTI). The UE 10 receives a random access response in a MAC Protocol Data Unit (PDU) on the PDSCH indicated by the detected PDCCH.

FIG. 5 b shows a connection process in an RRC layer.

As shown in FIG. 5 b , the RRC state is indicated depending on whether RRC is connected or not. The RRC state means whether or not the entity of the RRC layer of the UE 10 is in logical connection with the entity of the RRC layer of the eNodeB 20. A state that is connected is called an RRC connected state, and a state that is not connected is called an RRC idle state.

Since the UE 10 in the connected state has an RRC connection, the E-UTRAN can determine the existence of the corresponding UE on per cell, and thus can effectively control the UE 10. On the other hand, the UE 10 in the idle state cannot be detected by the eNodeB 20, and is managed by the core network in a tracking area unit, which is a larger area unit than the cell. The tracking area is an aggregate unit of cells. That is, only the existence of the UE 10 in the idle state is determined in a large area unit, and in order to receive a normal mobile communication service such as voice or data, the UE should transit to the connected state.

When the user turns on the UE 10 for the first time, the UE 10 first searches for an appropriate cell and then stays in an idle state in the corresponding cell. The UE 10, which stayed in the idle state, establishes an RRC connection with the RRC layer of the eNodeB 20 through an RRC connection procedure and transits to an RRC connected state only when it needs to establish an RRC connection.

There are several cases in which the UE in the idle state needs to establish an RRC connection, e.g., a user's call attempt or when uplink data transmission is required, or when a paging message is received from the E-UTRAN, for transmission of the response message.

In order for the UE 10 in the idle state to establish an RRC connection with the eNodeB 20, an RRC connection procedure should be performed as mentioned above. The RRC connection process includes, largely, a process in which the UE 10 transmits an RRC connection request message to the eNodeB 20, a process in which the eNodeB 20 transmits an RRC connection setup message to the UE 10, and a process in which the UE 10 transmits an RRC connection setup complete message to the eNodeB 20. This process will be described in more detail with reference to FIG. 5 b as follows.)

1) When the UE 10 in the idle state wants to establish an RRC connection for reasons such as a call attempt, a data transmission attempt, or a response to a paging of the eNodeB 20, first, the UE 10 transmits a RRC connection request message to the eNodeB 20.

2) Upon receiving the RRC connection request message from the UE 10, the eNB 20 accepts the RRC connection request of the UE 10 if the radio resources are sufficient, and transmits a RRC connection setup message as a response message to the UE 10.

3) Upon receiving the RRC connection setup message, the UE 10 transmits an RRC connection setup complete message to the eNodeB 20. When the UE 10 successfully transmits the RRC connection establishment message, the UE 10 establishes an RRC connection with the eNodeB 20 and transits to the RRC connected mode.

<Network Failure>

Meanwhile, a failure may occur in the base station of the first Public Land Mobile Network (PLMN) by the first operator, and a situation may occur in which a mobile communication service cannot be provided any longer through the corresponding base station.

A simple failure can be restored within a short period of time, but when a failure occurs due to fire, flooding, etc., it may not be restored for hours or days. In this case, simple communication may cause inconvenience to the user, but interruption of important communication (e.g., emergency call (119 or 911 call) or corporate Virtual Private Network (VPN) communication) may cause a major problem.

Therefore, when a failure occurs in the first PLMN by the first operator, another second operator should be able to provide services for subscribers of the first operator on behalf of the first operator.

However, there is a problem that a technical method for this has not been proposed so far.

SUMMARY

Accordingly, an object of the present specification is to propose a method for solving the above-described problems.

In order to achieve the above object, a disclosure of the present specification provides a method for a User Equipment (UE) subscribed to a first Public Land Mobile Network (PLMN) to perform access. The method may include transmitting a first request message to a network node via a base station. The base station may be a base station of a second PLMN that broadcasts system information including information of the first PLMN. The method may include receiving a first response message for the first request message from the network node. The first response message may include information informing that there is a service failure in the first PLMN. The method may include transmitting a second request message to the second PLMN or performing a procedure of reselecting another PLMN, instead of the first PLMN having the service failure, based on the first response message including the information.

The first response message may be an attach accept message or an attach reject message, based on the first request message being an attach request message. The first response message may be a registration accept message or a registration reject message, based on the first request message being a registration request message.

The procedure of reselecting another PLMN may be performed, based on the first request message being a registration request message and the first response message being a registration reject message.

The transmitting the second request message to the second PLMN may be performed, based on the first request message being a registration request message and the first response message being a registration accept message. The second request message may be a session establishment request message.

The method may further include receiving a second response message for the second request message. The second response message may include a session establishment accept message or a session establishment reject message, based on the second request message being a session establishment request message.

The session establishment reject message may include information informing that there is a service failure in the first PLMN.

The method may further include performing a deregistration procedure or a procedure of reselecting another PLMN, based on receiving the session establishment reject message including informing that there is a service failure in the first PLMN.

The method may further include transmitting a Session Initiation Protocol (SIP)- based request message to an IP Multimedia Subsystem (IMS) node, based on receiving the session establishment accept message, which is the second response message.

In order to achieve the above object, a disclosure of the present specification provides a User Equipment (UE) subscribed to a first Public Land Mobile Network (PLMN). The UE may include a transceiver, and a processor configured to control the transceiver. The processor may be configured to control the transceiver to transmit a first request message to a network node via a base station. The base station may be a base station of a second PLMN that broadcasts system information including information of the first PLMN. The processor may be configured to control the transceiver to receive a first response message for the first request message from the network node. The first response message may include information informing that there is a service failure in the first PLMN. The processor may be configured to transmit a second request message to the second PLMN or perform a procedure of reselecting another PLMN, instead of the first PLMN having the service failure, based on the first response message including the information.

According to the disclosure of the present specification, it is possible to solve the problems of the prior art.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a structure of an evolved mobile communication network.

FIG. 2 is an exemplary diagram showing the general functions of the main nodes of the E-UTRAN and the EPC.

FIG. 3 is an exemplary diagram showing the structure of a radio interface protocol in the control plane between the UE and the eNodeB.

FIG. 4 is another exemplary diagram showing the structure of a radio interface protocol in the user plane between the UE and the eNB.

FIG. 5 a is a flowchart illustrating a random access procedure in 3GPP LTE.

FIG. 5 b shows a connection process in an RRC layer.

FIG. 6 shows a connection between an EPC and an IP Multimedia Subsystem (IMS).

FIG. 7 is an exemplary diagram illustrating a roaming scheme of Voice over LTE (VoLTE).

FIG. 8 is an exemplary signal flow diagram illustrating a process of performing IMS registration in a HR scheme in a situation in which the UE roams to a visited network.

FIG. 9 is a structural diagram of a next-generation mobile communication network.

FIG. 10 shows an example of an expected structure of next-generation mobile communication from a node perspective.

FIG. 11 shows an example of an architecture for supporting simultaneous access to two data networks.

FIG. 12 is another exemplary diagram showing the structure of a radio interface protocol between the UE and the gNB.

FIG. 13 exemplarily shows a procedure for accepting a disaster roaming emergency call according to a disclosure of the present specification.

FIGS. 14 a and 14 b exemplarily show a procedure in which a disaster roaming emergency call is not allowed according to a disclosure of the present specification.

FIG. 15 exemplarily shows a procedure for accepting a disaster roaming emergency call according to another disclosure of the present specification.

FIGS. 16 a and 16 b exemplarily show a procedure in which a disaster roaming emergency call is not allowed according to another disclosure of the present specification.

FIG. 17 illustrates a wireless communication system according to an embodiment.

FIG. 18 illustrates a block diagram of a network node according to an embodiment.

FIG. 19 is a block diagram of a UE according to an embodiment.

FIG. 20 illustrates an example of 5G use scenarios.

FIG. 21 shows an AI system 1 according to an embodiment.

DETAILED DESCRIPTION

The technical terms used herein are used to merely describe specific embodiments and should not be construed as limiting the technical idea. Further, the technical terms used herein should be, unless defined otherwise, interpreted as having meanings generally understood by those skilled in the art but not too broadly or too narrowly. Further, the technical terms used herein, which are determined not to exactly represent the spirit of the disclosure, should be replaced by or understood by such technical terms as being able to be exactly understood by those skilled in the art. Further, the general terms used herein should be interpreted in the context as defined in the dictionary, but not in an excessively narrowed manner.

The expression of the singular number in the specification includes the meaning of the plural number unless the meaning of the singular number is definitely different from that of the plural number in the context. In the following description, the term “include” or “have” may represent the existence of a feature, a number, a step, an operation, a component, a part or the combination thereof described in the specification, and may not exclude the existence or addition of another feature, another number, another step, another operation, another component, another part or the combination thereof.

The terms “first” and “second” are used for the purpose of explanation about various components, and the components are not limited to the terms “first” and “second”. The terms “first” and “second” are only used to distinguish one component from another component. For example, a first component may be named as a second component without deviating from the scope of the present disclosure.

It will be understood that when an element or layer is referred to as being “connected to” or “coupled to” another element or layer, it can be directly connected or coupled to the other element or layer or intervening elements or layers may be present. In contrast, when an element is referred to as being “directly connected to” or “directly coupled to” another element or layer, there are no intervening elements or layers present.

Hereinafter, exemplary embodiments of the present disclosure will be described in greater detail with reference to the accompanying drawings. In describing the present disclosure, for ease of understanding, the same reference numerals are used to denote the same components throughout the drawings, and repetitive description on the same components will be omitted. Detailed description on well-known arts which are determined to make the gist of the disclosure unclear will be omitted. The accompanying drawings are provided to merely make the spirit of the disclosure readily understood, but not should be intended to be limiting of the disclosure. It should be understood that the spirit of the disclosure may be expanded to its modifications, replacements or equivalents in addition to what is shown in the drawings.

In the drawings, User Equipments (UEs) are shown for example. The UE may also be denoted a terminal or Mobile Equipment (ME), etc. The UE may be a portable device such as a laptop computer, a mobile phone, a PDA, a smartphone, a multimedia device, etc., or may be a stationary device such as a PC or a car mounted device.

<Definition of Terms>

For a better understanding, the terms used herein are briefly defined before going to the detailed description of the disclosure with reference to the accompanying drawings.

-   -   GERAN: An abbreviation of GSM EDGE Radio Access Network, which         refers to a radio access section connecting the core network of         GSM/EDGE and the UE.     -   UTRAN: Abbreviation for Universal Terrestrial Radio Access         Network, which refers to a radio access section connecting the         core network of 3G mobile communication and the UE.     -   E-UTRAN: An abbreviation of Evolved Universal Terrestrial Radio         Access Network, which refers to a radio access section         connecting the core network of the 4th generation mobile         communication, i.e., LTE, and the UE.     -   UMTS: Abbreviation for Universal Mobile Telecommunication         System, which refers to the core network of 3G mobile         communication.     -   UE/MS: An abbreviation of User Equipment/Mobile Station, which         refers to a terminal device.     -   EPS: An abbreviation of an Evolved Packet System, which refers         to a core network supporting a Long Term Evolution (LTE) network         and to a network evolved from an UMTS.     -   PDN: An abbreviation of a Public Data Network, which refers to         an independent network where a server for providing service is         placed.     -   PDN connection: A connection from UE to a PDN, i.e., an         association (or connection) between UE represented by an IP         address and a PDN represented by an APN.     -   PDN-GW (Packet Data Network Gateway): A network node of an EPS         network which performs functions of UE IP address allocation,         packet screening & filtering, and charging data collection.     -   S-GW (Serving Gateway): A network node of an EPS network which         performs functions of mobility anchor, packet routing, idle mode         packet buffering, and triggering an MME to page UE.     -   PCRF (Policy and Charging Rule Function): A node of an EPS         network which performs policy decision to dynamically apply QoS         and charging policies differentiated for each service flow     -   APN (Access Point Name): A name of an access point that is         managed in a network and provided to UE. That is, an APN is a         character string that denotes or identifies a PDN. While         requested service or a network (PDN) is accessed via P-GW, an         APN is a name (a character string) previously defined within a         network to search the so that the corresponding P-GW can be         searched for (e.g., ‘internet.mnc012.mcc345.gprs’).     -   TEID (Tunnel Endpoint Identifier): End point ID of the tunnel         established between nodes in the network, and configured for         each section per bearer of each UE.

NodeB: A base station of an UMTS network and is installed outdoors, of which cell coverage corresponds to a macro cell.

eNodeB: A base station of an Evolved Packet System (EPS) and is installed outdoors, of which cell coverage corresponds to a macro cell.

(e)NodeB: A term referring to NodeB and eNodeB.

-   -   MME: An abbreviation of a Mobility Management Entity, and         performs functions of controlling each entity within an EPS in         order to provide a session and mobility for UE.     -   A session: A path for data transmission, and a unit thereof may         be a PDN, a bearer, or an IP flow unit. The units may be         classified into, as defined in 3GPP, a unit of the entire target         network (i.e., an APN or PDN unit), a unit classified based on         QoS within the entire target network (i.e., a bearer unit), and         a destination IP address unit.     -   PDN connection: A connection from UE to a PDN, i.e., an         association (or connection) between UE represented by an IP         address and a PDN represented by an APN. It means a connection         between entities (i.e., UE-PDN GW) within a core network so that         a session can be formed.     -   UE context: Information about the situation of UE which is used         to manage the UE in a network, i.e., situation information         including an UE ID, mobility (e.g., a current location), and the         attributes of a session (e.g., QoS and priority, etc.)     -   NAS (Non-Access-Stratum): A higher stratum of a control plane         between a UE and an MME. The NAS supports mobility management,         session management, IP address management, etc., between the UE         and the network.     -   RAT: An abbreviation of Radio Access Technology, which means         GERAN, UTRAN, E-UTRAN, etc.

Meanwhile, the embodiments presented below may be implemented alone, but may be implemented as a combination of several embodiments.

FIG. 6 shows a connection between an EPC and an IP Multimedia Subsystem (IMS).

Referring to FIG. 6 , in the EPC, the MME 510, the S-GW 520, the P-GW 530 a connected to the IMS, the P-GW 530 b connected to the Internet, the Policy and Charging Rule Function (PCRF) 580 connected to the P-GW 530 b, and the Traffic Detection Function (TDF) 590 connected to the PCRF 580 are shown.

The TDF 590 detects the application and reports the detected application and description information about the service data flow of the application to the PCRF 580. The TDF 590 supports solicited application reporting and/or unsolicited application reporting.

IMS is a network technology that enables Packet Switching (PS) based on Internet Protocol (IP) to not only wired terminals but also wireless terminals. It has been proposed to connect both wired terminals and wireless terminal via IP (i.e., All-IP).

The IMS-based network includes Call Session Control Function (CSCF) and Interconnection Border Control Functions (IBCF) 620 for handling procedures for control signaling, registration, and session. The CSCF may include a Proxy-CSCF (P-CSCF) 610 and a Serving-CSCF (S-CSCF) 630. In addition, the CSCF may include an Interrogating-CSCF (I-CSCF). The P-CSCF 610 operates as a first access point for UE in an IMS-based network. Then, the S-CSCF 630 processes a session in the IMS network. That is, the S-SCSF 630 is an entity responsible for routing signaling, and routes a session in the IMS network. And, the I-CSCF operates as an access point with other entities in the IMS network.

Under the above IMS, an IP-based session is controlled by a Session Initiation Protocol (SIP). The SIP is a protocol for controlling a session, and is a signaling protocol that specifies a procedure for UEs wanting to communicate to identify each other and find their location, create a multimedia service session between them, or delete and change the created session. The SIP uses a SIP Uniform Resource Identifier (URI) similar to an e-mail address to distinguish each user, so that a service can be provided without being dependent on an IP address. These SIP messages are control messages, but are transmitted between the UE and the IMS network through the EPC user plane.

Referring to FIG. 6 , the first P-GW 530 a of the EPC is connected to the P-CSCF 610 of the IMS, the P-CSCF 610 is connected to the IBCF 620, and the IBCF 620 is connected to the S-CSCF 630.

In addition, the second P-GW 530 b of the EPC is connected to the network of the Internet service provider.

FIG. 7 is an exemplary diagram illustrating a roaming scheme of Voice over LTE (VoLTE).

As can be seen with reference to FIG. 7 , in VoLTE roaming methods, there are a Home Routed (HR) scheme and a Local Breakout (LBO) scheme.

According to the LBO scheme, the IMS signaling transmitted from the UE goes through the S-GW/P-GW/P-CSCF in the Visited Public Land Mobile Network (V-PLMN), and is forwarded to the S-CSCF in the Home PLMN (H-PLMN).

In the HR scheme, the IMS signaling transmitted from the UE goes through the S-GW in the V-PLMN, the P-GW/P-CSCF in the H-PLMN, and then forwarded to the S-CSCF.

FIG. 8 is an exemplary signal flow diagram illustrating a process of performing IMS registration in a HR scheme in a situation in which the UE roams to a visited network.

As can be seen with reference to FIG. 8 , the UE 100 is in a roaming state in the visited network.

First, the UE 100 located in the visited network generates an IMS PDN with a P-GW in the home network through the S-GW 520 b in the visited network. Here, the IMS PDN may be a PDN for an IMS service, a PDN of a well-known IMS APN, or a PDN for a Voice over LTE service.

1) Next, when the UE 100 transmits a SIP-based REGISTER message to the S-GW 520 b in the visited network to perform IMS registration, the S-GW 520 b in the visited network forwards the message to the P-CSCF 610 a in the home network.

2) The P-CSCF 610 a forwards the message to the I-CSCF 640 a.

3)˜4) The I-CSCF 640 a obtains user information from the HSS 540 a in the home network.

5) Next, the I-CSCF 640 a transmits the SIP-based REGISTER message to the S-CSCF 630 a.

6)˜7) The S-CSCF 630 a obtains user information from the HSS.

8) Subsequently, the S-CSCF 630 a performs service control for registration of the UE.

9)˜11) If the registration of the UE is successful, the S-CSCF 630 a transmits a 200 OK message.

<Structure of Next-Generation Mobile Communication>

With the success of Long Term Evolution (LTE)/LTE-Advanced (LTE-A) for the 4th generation mobile communication, more interest is rising to the next generation, i.e., 5th generation (also known as 5G) mobile communication and extensive research and development are being carried out accordingly.

The 5G mobile communication defined in the International Telecommunication Union (ITU) provides a data transfer rate of up to 20 Gbps and a sensible transfer rate of at least 100 Mbps anytime anywhere. ‘IMT-2020’ is a formal name, and aims to be commercialized in the year 2020 worldwide.

The ITU proposes three usage scenarios, e.g., enhanced Mobile BroadBand (eMBB), massive Machine Type Communication (mMTC), and Ultra Reliable and Low Latency Communications (URLLC).

First, the URLLC relates to a usage scenario which requires a high reliability and a low latency. For example, a service such as autonomous driving, factory automation, and augmented reality requires a high reliability and a low latency (e.g., a latency less than or equal to lms). At present, a latency of 4G (LTE) is statistically 21-43 ms (best 10%), 33-75 ms (median). This is insufficient to support a service requiring the latency less than or equal to 1 ms.

Next, an eMBB usage scenario relates to a usage scenario requiring a mobile ultra-wide band.

It seems that a core network designed for the existing LTE/LTE-A has difficulty in accommodating a high-speed service of the ultra-wide band.

Therefore, it is urgently required to re-design the core network in 5G mobile communication.

FIG. 9 is a structural diagram of a next-generation mobile communication network.

5G Core (5GC) may include various components. In FIG. 9 , 5GC includes Access and mobility Management Function (AMF) 410, Session Management Function (SMF) 420, Policy Control Function (PCF) 430, User Plane Function (UPF) 440, Application Function (AF) 450 , Unified Data Management (UDM) 460 , and Non-3GPP InterWorking Function (N3IWF) 490, which correspond to some of them.

The UE 100 is connected to a data network through the UPF 450 through a Next Generation Radio Access Network (NG-RAN).

The UE 100 may be provided with a data service through untrusted non-3GPP access, e.g., Wireless Local Area Network (WLAN). To connect the non-3GPP access to the core network, N3IWF 490 may be deployed.

FIG. 10 shows an example of an expected structure of next-generation mobile communication from a node perspective.

As can be seen with reference to FIG. 10 , a UE is connected to a data network (DN) via a next generation Radio Access Network (RAN).

The illustrated Control Plane Function (CPF) node performs functions of the entirety or part of a Mobility Management Entity (MME) of 4G mobile communication and control plane functions of the entirety or part of a Serving Gateway (S-GW) and PDN gateway (P-GW) of 4G mobile communication. The CPF node includes an Access and mobility Management Function (AMF) and a Session Management Function (SMF).

The illustrated User Plane Function (UPF) node is a type of a gateway through which user data is transmitted/received. The UPF node may perform user plane functions of the entirety or part of an S-GW or P-GW of 4G mobile communication.

The illustrated Policy Control Function (PCF) is a node which controls a provider's policy.

The illustrated Application Function (AF) is a server for providing several services to the UE.

The illustrated Unified Data Management (UDM) is a type of a server which manages subscriber information, like a Home Subscriber Server (HSS) of 4G mobile communication. The UDM stores the subscriber information in a Unified Data Repository (UDR) and manages it.

The illustrated Authentication Server Function (AUSF) authenticates and manages the UE.

The illustrated Network Slice Selection Function (NSSF) is a node for network slicing as described below.

In FIG. 10 , the UE can simultaneously access two data networks by using multiple Protocol Data Unit (PDU) sessions.

FIG. 11 shows an example of an architecture for supporting simultaneous access to two data networks.

FIG. 11 shows an architecture for a UE to simultaneously access two data networks using one PDU session.

FIG. 12 is another exemplary diagram showing the structure of a radio interface protocol between the UE and the gNB.

The radio interface protocol is based on the 3GPP radio access network standard. The radio interface protocol is horizontally composed of a physical layer, a data link layer, and a network layer, and is vertically divided into a user plane for transmitting data information and a control plane for transmitting a control signal.

The protocol layers may be divided into L1 (Layer 1), L2 (Layer 2), and L3 (Layer 3) based on the lower three layers of the Open System Interconnection (OSI) reference model widely known in communication systems.

Meanwhile, in FIG. 12 , the RRC layer, the RLC layer, the MAC layer, and the PHY layer located below the NAS layer are collectively referred to as an Access Stratum (AS).

<Problems to be Solved by the Disclosure of the Present Specification>

The present specification describes a situation in which a failure occurs in the base station of the first PLMN by the first operator so that the mobile communication service can no longer be provided through the corresponding base station. It is assumed that, temporarily (e.g., hours or days, etc.) until the physical recovery of the corresponding base station is made, the base station of the second PLMN by the second operator broadcasts SIB by including information on the first PLMN by a third party (i.e., the first operator) in order to provide services on behalf of the first operator in the affected area.

In this case, the third-party subscription UE receiving the broadcast information accesses the network in the same way as accessing the HPLMN, whereas the network provides a form of servicing a roaming UE. That is, the UE may attempt to connect to the second PLMN, such as performing a connection to a network node of the first PLMN (e.g., HPLMN). To this end, the network node of the second PLMN may perform an interaction with the first PLMN. Therefore, a route such as Home Routed (HR) roaming may be used. This may cause the following problems.

When the UE attempts an emergency call, a PDN connection for an emergency call is established in the core network of the serving PLMN (e.g., the first PLMN) for connection to the emergency call center of the serving PLMN (e.g., the first PLMN).

The subscriber of the first PLMN suffering from base station failure requests an emergency call via the base station of the second PLMN that is currently temporarily coping with the failure. At this time, the UE can recognize that it is being served by the first PLMN, but the core network supporting the service is actually the second PLMN that temporarily copes with the current failure. Accordingly, the serving PLMN of the UE may be the second PLMN. The network control node of the second PLMN may not process emergency calls for each PLMN, but intend to connect all emergency calls to the emergency call center in its PLMN.

Therefore, there is a need for an effective method for reducing the effect on the load of the second PLMN, which is temporarily coping with the current failure. This can be one of the measures to minimize the impact on the service of the existing subscribers of the second PLMN, which is temporarily coping with the current failure.

<Disclosure of the Present Specification>

The disclosure of the present specification may be implemented by a combination of one or more of the following configurations. In the case of the embodiment below, an embodiment is shown to show each individual configuration, but an embodiment in which one or more combinations are configured together may be implemented.

Hereinafter, an EPS-based embodiment will be described, but the content disclosed by the present specification is also applicable to an embodiment implemented in SGS.

In the present specification, a special roaming situation mode of the UE (i.e., not a normal roaming situation, but a roaming situation that operates to overcome the failure situation as described above) is defined. For ease of description in the present specification, general roaming will be referred to as N-roaming, and roaming that operates to overcome the failure situation will be referred to as S-roaming

As mentioned above, if the UE does not understand the S-roaming situation, it recognizes it as a non-roaming situation and operates. If the UE recognizes the S-roaming situation according to the contents to be described later, the UE operates in the S-roaming mode preset by the operator. The operator's settings may be pre-configured or transmitted to the UE through an Open Mobile Alliance (OMA)-Device Management (DM) scheme or a policy delivery scheme. The operator's settings may be updated as necessary.

For example, in the S-roaming situation, the operator may allow requests for voice and SMS, may limit requests for data service, or may set the priority of a specific access available for a specific application differently from the general situation. Alternatively, for the purpose of adjusting the signal load, the operator may change the period of the Periodic Tracking Area Update (P-TAU), or may set the non- essential request from the periodic operation to be delayed.

Hereinafter, a method according to a disclosure of the present specification for effectively supporting/handling an emergency call in a failure situation is described.

I. A method for handling emergency calls in the second PLMN that is temporarily coping with failures

I-1. Operation of network nodes of the second PLMN, e.g., MME or AMF

The network node, e.g., MME or AMF, receives an emergency call request message transmitted by the UE.

The network node, e.g., MME or AMF, recognizes that it is an emergency call. In addition, by checking subscriber information and roaming agreement, etc., the network node, e.g., MME or AMF, confirms that the UE is a subscriber of another PLMN having a disaster roaming agreement.

According to the disaster roaming agreement, the network node, e.g., MME or AMF, applies and controls emergency call policies for each PLMN according to disaster roaming That is, the network node, e.g., MME or AMF, may decide to process an emergency call in its own PLMN for a subscriber of a specific PLMN.

If the network node is an MME, the MME accepts an emergency attach request message for connection to an emergency call service center, and accepts an emergency PDN connection request message. Alternatively, if the network node is an AMF, the AMF accepts a registration request message for connection to an emergency call service center, and accepts an emergency PDU session establishment request message.

The network node, e.g., MME or AMF, adds information indicating the S-roaming situation additionally to the PDN connection accept message or the PDU session establishment accept message. This may be used for the purpose of notifying the user of the current situation through UI/UX. In parallel with this process, the network node may notify the user of the S-roaming situation through a separate SMS service, etc.

1-2. Operation of a Network Node of the Second PLMN, e.g., P-CSCF

A network node (e.g., P-CSCF) identifies PLMN ID and cell information, based on P-Access-Network-Info (PANI) information included in a Session Initiation Protocol (SIP)-based message (e.g., IMS emergency registration message) transmitted by the UE for an IMS emergency call.

In addition, according to UE implementations (based on the operator's preset policy) or according to SIP-based indication proposed in the present specification, the following internal operation of the UE may be performed. This information may explicitly inform S-roaming, or it may be information that allows the UE to perform a specific intended operation by implicit information.

A) The UE transmits a message including information of the first PLMN based on the information received from the base station.

B) Alternatively, the UE transmits a message including information of the second PLMN based on the information received from the base station.

The P-CSCF recognizes that the PLMN information to which it belongs and the PLMN information of the UE obtained from the PANI are the same/different, so that it can be recognized as a non-roaming situation or a general roaming situation to another PLMN.

Depending on whether the UE performs operation A or operation B, a mechanism for distinguishing the general roaming situation and the non-roaming situation is required.

Option 1: A disaster roaming situation may be recognized based on the information that access is made from a specific time/specific PLMN by the operator's setting information.

Option 2: Events that can perform specific mechanisms can be preset in the network by the operator. That is, the MME or the AMF that is aware of the disaster roaming situation via the P-GW/S-GW of the EPC or the SMF of the 5GC checks the S-roaming situation through a question/response process. In addition, such information may be stored.

According to the charging policy of the operator, the P-CSCF may perform the IMS registration procedure, etc., by including the newly set PLMN information, such as changing to the serving PLMN information instead of the PLMN information in the PANI information.

Additionally, the network may not only notify the UE of the S-roaming situation, but may also perform more active actions. For example, the network may provide PLMN information that should be used in the procedure for an IMS emergency call. The UE that has received this information (i.e., the UE that recognizes S-roaming and supports the corresponding function) provides the PLMN information received from the network in order to request an emergency call thereafter. In addition, the network may notify the information along with valid time information or may also provide a mechanism to revoke/update the information provided.

FIG. 13 exemplarily shows a procedure for accepting a disaster roaming emergency call according to a disclosure of the present specification.

The exemplary procedure shown in FIG. 13 is described based on the following assumptions.

First, the first PLMN is the Home PLMN (HPLMN) of the UE and is in a communication service unavailable state due to the occurrence of a communication disaster. The base station of the second PLMN may temporarily broadcast information of the first PLMN according to a preset policy and an operator command, e.g., Operation, Administration and Management (OAM) command This is a policy of the operator considering the effect of allowing the UE to recognize the base station of the second PLMN as the base station of the first PLMN and perform an access attempt operation.

Hereinafter, it will be described with reference to the drawings.

0) Upon recognizing the failure of the first PLMN by the first operator, the second operator of the second PLMN decides to provide a service on behalf of the first operator. Then, the base station of the second PLMN broadcasts a System Information Block (SIB) including information on the first PLMN.

1) The UE transmits an emergency registration request message or a general registration request message to attempt access to a second PLMN that broadcasts information of the first PLMN. The message is transmitted to the AMF of the second PLMN via the base station of the second PLMN.

2) The AMF of the second PLMN evaluates whether there is a disaster roaming In order to check the subscriber information of the accessing UE, an interaction is performed with the UDM of the HPLMN, i.e., the first PLMN, and preset operator policies and roaming policies are checked. If necessary, interaction with another network node such as PCF for checking operator policies may be performed.

Through this process, the AMF of the second PLMN determines whether to accept the access for providing the emergency roaming service of the access requesting UE and the range of the disaster roaming service that can be provided (e.g., basic voice call and specific service, etc.), etc.

In particular, the AMF of the second PLMN determines how to process the emergency disaster roaming call. That is, the AMF of the second PLMN may determine not only whether to accept the emergency call, but also whether to process the emergency call in the second PLMN that is the local PLMN (or serving PLMN) or in the first PLMN that is the HPLMN.

3) The AMF of the second PLMN transmits a registration accept message to the UE. In this case, information on disaster roaming may be explicitly or implicitly included.

Based on this information, the UE may change the operation mode to the disaster roaming mode and start applying the preset disaster roaming policy.

4) The UE transmits an emergency PDU session establishment request message to the SMF via the AMF. According to the determined emergency call processing scheme, the network node establishes a PDU session. In this example, it is assumed that processing in the local PLMN, i.e., the second PLMN.

5) The network node, i.e., the SMF, informs the UE of successful establishment of the emergency PDU session. Specifically, the network node, i.e., the SMF, transmits an emergency PDU session establishment accept message to the UE.

6) The UE transmits an emergency IMS registration request signaling to an IMS node, e.g., P-CSCF, through the established PDU session. In this example, since processing in the serving PLMN is assumed, the signaling is transmitted to the IMS node, i.e., the P-CSCF, of the second PLMN through the UPF of the second PLMN.

7) The IMS network node, i.e., the P-CSCF, recognizes the PLMN information, operates according to the disaster roaming policy, such as changing the PLMN information if necessary, and performs procedures for IMS registration and session establishment.

8) The IMS node, i.e., the P-CSCF, transmits a success response for the IMS registration procedure to the UE. That is, an IMS emergency request accept message may be transmitted to the UE. The message may include information on disaster roaming explicitly or implicitly.

FIGS. 14 a and 14 b exemplarily show a procedure in which a disaster roaming emergency call is not allowed according to a disclosure of the present specification.

The exemplary procedure shown in FIGS. 14 a and 14 b is described based on the following assumptions.

First, the first PLMN is in a communication service unavailable state due to the occurrence of a communication disaster. The base station of the second PLMN may temporarily broadcast information of the first PLMN according to a preset policy and an operator command, e.g., Operation, Administration and Management (OAM) command This is a policy of the operator considering the effect of allowing the UE to recognize the base station of the second PLMN as the base station of the first PLMN and perform an access attempt operation to the second PLMN.

0) Upon recognizing the failure of the first PLMN by the first operator, the second operator of the second PLMN decides to provide a service on behalf of the first operator. Then, the base station of the second PLMN broadcasts a System Information Block (SIB) including information on the first PLMN.

1) The UE transmits an emergency registration request message or a general registration request message to attempt access to a second PLMN. The message is transmitted to the AMF of the second PLMN via the base station of the second PLMN.

2) The AMF of the second PLMN evaluates whether there is a disaster roaming In order to check the subscriber information of the accessing UE, an interaction is performed with the UDM of the HPLMN, i.e., the first PLMN, and preset operator policies and roaming policies are checked. If necessary, interaction with another network node such as PCF for checking operator policies may be performed.

Through this process, the AMF of the second PLMN determines whether to accept the access for providing the emergency roaming service of the access requesting UE and the range of the disaster roaming service that can be provided (e.g., basic voice call and specific service, etc.), etc.

In particular, the AMF of the second PLMN determines how to process the emergency disaster roaming call. That is, the AMF of the second PLMN may determine not only whether to accept the emergency call, but also whether to process the emergency call in the second PLMN or in the first PLMN that is the HPLMN.

According to the illustrated case B-1, the following procedure is performed.

3) The AMF of the second PLMN transmits a registration reject message to the UE.

In this case, information on disaster roaming may be explicitly or implicitly included in the registration reject message.

4) Upon receiving the reject message, the UE evaluates the rejection cause of the message, and then performs a PLMN re-selection procedure. In this case, the UE manages the priority of the PLMN based on the received information on disaster roaming For example, for a PLMN in which disaster roaming has occurred, control such as lowering the priority of the corresponding PLMN temporarily/for a specific time is included.

Alternatively, the UE may attempt another method for emergency call processing, such as performing a procedure for attempting an emergency call to the CS domain

According to the illustrated case B-2, the following procedure is performed.

3) The AMF of the second PLMN transmits a registration accept message to the UE.

In this case, information on disaster roaming may be explicitly or implicitly included in the registration accept message.

Based on this information, the UE may change the operation mode to the disaster roaming mode and start applying the preset disaster roaming policy.

4) The UE transmits an emergency PDU session establishment request message to the SMF via the AMF. In this example, it is assumed that the SMF of the local PLMN, i.e., the second PLMN, processes the emergency PDU session establishment request message.

5) The SMF of the second PLMN may perform additional disaster roaming evaluation. That is, the SMF may grant a service only for a specific session, and may determine the range of the service to be granted accordingly.

6) The SMF of the second PLMN transmits an emergency PDU session establishment reject message to the UE. The reject message may include disaster roaming related information.

7) Upon receiving the reject message for establishing the emergency PDU session for the emergency call, the UE may evaluate the rejection cause of the message. In addition, the UE may perform de-registration and PLMN reselection procedures. In this case, the UE may manage the priority of the PLMN, based on the disaster roaming related information included in the reject message. For example, for a PLMN in which disaster roaming has occurred, control such as lowering the priority of the corresponding PLMN temporarily/for a specific time is included.

Alternatively, the UE may attempt another method for emergency call processing, such as performing a procedure for attempting an emergency call to the CS domain

II. A method for handling emergency calls on subscriber's HPLMN in accordance with the disaster roaming agreement

II-1. Operation of network nodes, e.g., as MME or AMF

The network node, e.g., MME or AMF, receives the emergency call request message transmitted by the UE.

The network node, e.g., MME or AMF, recognizes that it is an emergency call. In addition, by checking subscriber information and roaming agreement, etc., the network node, e.g., MME or AMF, confirms that the UE is a subscriber of another PLMN having a disaster roaming agreement.

According to the disaster roaming agreement, the network node, e.g., MME or AMF, applies and controls emergency call policies for each PLMN according to disaster roaming That is, the network node, e.g., MME or AMF, may decide to process an emergency call in its own PLMN for a subscriber of a specific PLMN. That is, in case of EPC, a roaming may be performed in an HR scheme connected to the S-GW of the serving PLMN and the P-GW of the HPLMN. In case of SGC, a roaming may be performed in an HR scheme connected to the UPF of the serving PLMN and the UPF of the HPLMN based on the control of the AMF/SMF of the serving PLMN and the SMF of the HPLMN.

For reference, if the UE does not perform disaster roaming but is identified as a general inbound roamer, the network node, e.g., MME or AMF, decides to process an emergency call in the corresponding PLMN like a non-roaming subscriber.

If the network node is an MME, the MME accepts an emergency attach request message for connection to an emergency call service center, and accepts an emergency PDN connection request message. Alternatively, if the network node is an AMF, the AMF accepts a registration request message for connection to an emergency call service center, and accepts an emergency PDU session establishment request message.

The network node, e.g., MME or AMF, adds information indicating the S-roaming situation additionally to the PDN connection accept message or the PDU session establishment accept message. This may be used for the purpose of notifying the user of the current situation through UI/UX. In parallel with this process, the network node may notify the user of the S-roaming situation through a separate SMS service, etc.

11-2. Operation of a Network Node of the HPLMN, e.g., P-CSCF

A network node (e.g., P-CSCF) identifies PLMN ID and cell information, based on P-Access-Network-Info (PANI) information included in a SIP message (e.g., IMS emergency registration message) transmitted by the UE for an IMS emergency call.

In addition, according to UE implementations (based on the operator's preset policy) or according to SIP-based indication proposed in the present specification, the following internal operation of the UE may be performed. This information may explicitly inform S-roaming, or it may be information that allows the UE to perform a specific intended operation by implicit information.

A) The UE transmits a message including information of the first PLMN based on the information received from the base station.

B) Alternatively, the UE transmits a message including information of the second PLMN based on the information received from the base station.

The P-CSCF recognizes that the PLMN information to which it belongs and the PLMN information of the UE obtained from the PANI are the same/different, so that it can be recognized as a non-roaming situation or a general roaming situation to another PLMN.

Depending on whether the UE performs operation A or operation B, a mechanism for distinguishing the general roaming situation and the non-roaming situation is required. Or, a mechanism for distinguishing from the general roaming situation is needed.

Option 1: A disaster roaming situation may be recognized based on the information that access is made from a specific time/specific cell by the operator's setting information.

Option 2: Events that can perform specific mechanisms can be preset in the network by the operator. That is, the MME or the AMF that is aware of the disaster roaming situation via the P-GW/S-GW of the EPC or the SMF of the 5GC checks the S-roaming situation through a question/response process. In addition, such information may be stored.

According to the charging policy of the operator, the P-CSCF may perform the IMS registration procedure, etc., by including the newly set PLMN information, such as changing to the serving PLMN information instead of the PLMN information in the PANI information.

Additionally, the network may not only notify the UE of the S-roaming situation, but may also perform more active actions. For example, the network may provide PLMN information that should be used in the procedure for an IMS emergency call. The UE that has received this information (i.e., the UE that recognizes S-roaming and supports the corresponding function) provides the PLMN information received from the network in order to request an emergency call thereafter. In addition, the network may notify the information along with valid time information or may also provide a mechanism to revoke/update the information provided.

FIG. 15 exemplarily shows a procedure for accepting a disaster roaming emergency call according to another disclosure of the present specification.

The exemplary procedure shown in FIG. 15 is described based on the following assumptions.

First, the first PLMN is the Home PLMN (HPLMN) of the UE and is in a communication service unavailable state due to the occurrence of a communication disaster. The base station of the second PLMN may temporarily broadcast information of the first PLMN according to a preset policy and an operator command, e.g., Operation, Administration and Management (OAM) command This is a policy of the operator considering the effect of allowing the UE to recognize the base station of the second PLMN as the base station of the first PLMN and perform an access attempt operation.

Hereinafter, it will be described with reference to the drawings.

0) Upon recognizing the failure of the first PLMN by the first operator, the second operator of the second PLMN decides to provide a service on behalf of the first operator. Then, the base station of the second PLMN broadcasts a System Information Block (SIB) including information on the first PLMN.

1) The UE transmits an emergency registration request message or a general registration request message to attempt access to a second PLMN that broadcasts information of the first PLMN. The message is transmitted to the AMF of the second PLMN via the base station of the second PLMN.

2) The AMF of the second PLMN evaluates whether there is a disaster roaming In order to check the subscriber information of the accessing UE, an interaction is performed with the UDM of the HPLMN, i.e., the first PLMN, and preset operator policies and roaming policies are checked. If necessary, interaction with another network node such as PCF for checking operator policies may be performed.

Through this process, the AMF of the second PLMN determines whether to accept the access for providing the emergency roaming service of the access requesting UE and the range of the disaster roaming service that can be provided (e.g., basic voice call and specific service, etc.), etc.

In particular, the AMF of the second PLMN determines how to process the emergency disaster roaming call. That is, the AMF of the second PLMN may determine not only whether to accept the emergency call, but also whether to process the emergency call in the second PLMN that is the local PLMN (or serving PLMN) or in the first PLMN that is the HPLMN.

3) The AMF of the second PLMN transmits a registration accept message to the UE. In this case, information on disaster roaming may be explicitly or implicitly included.

Based on this information, the UE may change the operation mode to the disaster roaming mode and start applying the preset disaster roaming policy.

4) The UE transmits an emergency PDU session establishment request message to the SMF via the AMF. According to the determined emergency call processing scheme, the network node establishes a PDU session. In this example, it is assumed that processing in the HPLMN, i.e., the first PLMN. Accordingly, the SMF of the second PLMN exchanges messages necessary for establishing a PDU session with the SMF of the first PLMN, which is the HPLMN of the UE.

5) The SMF of the first PLMN informs the UE of successful establishment of the emergency PDU session. Specifically, the SMF of the first PLMN transmits an emergency PDU session establishment accept message to the UE.

6) The UE transmits an emergency IMS registration request signaling to an IMS node, e.g., P-CSCF, through the established PDU session. In this example, since processing in the first PLMN, which is the HPLMN, is assumed, the signaling is transmitted to the IMS node, i.e., the P-CSCF, of the first PLMN through the UPF of the second PLMN and the UPF of the first PLMN.

7) The IMS network node, i.e., the P-CSCF, recognizes the PLMN information, operates according to the disaster roaming policy, such as changing the PLMN information if necessary, and performs procedures for IMS registration and session establishment.

8) The IMS node, i.e., the P-CSCF, transmits a success response for the IMS registration procedure to the UE. That is, an IMS emergency request accept message may be transmitted to the UE. The message may include information on disaster roaming explicitly or implicitly.

FIGS. 16 a and 16 b exemplarily show a procedure in which a disaster roaming emergency call is not allowed according to another disclosure of the present specification.

The exemplary procedure shown in FIGS. 16 a and 16 b is described based on the following assumptions.

First, the first PLMN is in a communication service unavailable state due to the occurrence of a communication disaster. The base station of the second PLMN may temporarily broadcast information of the first PLMN according to a preset policy and an operator command, e.g., Operation, Administration and Management (OAM) command This is a policy of the operator considering the effect of allowing the UE to recognize the base station of the second PLMN as the base station of the first PLMN and perform an access attempt operation to the second PLMN.

0) Upon recognizing the failure of the first PLMN by the first operator, the second operator of the second PLMN decides to provide a service on behalf of the first operator. Then, the base station of the second PLMN broadcasts a System Information Block (SIB) including information on the first PLMN.

1) The UE transmits an emergency registration request message or a general registration request message to attempt access to a second PLMN. The message is transmitted to the AMF of the second PLMN via the base station of the second PLMN.

2) The AMF of the second PLMN evaluates whether there is a disaster roaming In order to check the subscriber information of the accessing UE, an interaction is performed with the UDM of the HPLMN, i.e., the first PLMN, and preset operator policies and roaming policies are checked. If necessary, interaction with another network node such as PCF for checking operator policies may be performed.

Through this process, the AMF of the second PLMN determines whether to accept the access for providing the emergency roaming service of the access requesting UE and the range of the disaster roaming service that can be provided (e.g., basic voice call and specific service, etc.), etc.

In particular, the AMF of the second PLMN determines how to process the emergency disaster roaming call. That is, the AMF of the second PLMN may determine not only whether to accept the emergency call, but also whether to process the emergency call in the second PLMN or in the first PLMN that is the HPLMN.

According to the illustrated case D-1, the following procedure is performed.

3) The AMF of the second PLMN transmits a registration reject message to the UE. In this case, information on disaster roaming may be explicitly or implicitly included in the registration reject message.

4) Upon receiving the reject message, the UE evaluates the rejection cause of the message, and then performs a PLMN re-selection procedure. In this case, the UE manages the priority of the PLMN based on the received information on disaster roaming For example, for a PLMN in which disaster roaming has occurred, control such as lowering the priority of the corresponding PLMN temporarily/for a specific time is included.

Alternatively, the UE may attempt another method for emergency call processing, such as performing a procedure for attempting an emergency call to the CS domain

According to the illustrated case D-2, the following procedure is performed.

3) The AMF of the second PLMN transmits a registration accept message to the UE. In this case, information on disaster roaming may be explicitly or implicitly included in the registration accept message.

Based on this information, the UE may change the operation mode to the disaster roaming mode and start applying the preset disaster roaming policy.

4) The UE transmits an emergency PDU session establishment request message to the SMF of the second PLMN. In this example, since processing in the first PLMN, which is the HPLMN, is assumed, the SMF of the second PLMN transmits the emergency PDU session establishment request message of the UE to the SMF of the first PLMN.

5) The SMF of the first PLMN, which is the HPLMN, may perform additional disaster roaming evaluation. That is, the SMF may grant a service only for a specific session, and may determine the range of the service to be granted accordingly.

6) The SMF of the first PLMN transmits an emergency PDU session establishment reject message to the UE. The reject message may include disaster roaming related information.

7) Upon receiving the reject message for establishing the emergency PDU session for the emergency call, the UE may evaluate the rejection cause of the message. In addition, the UE may perform de-registration and PLMN reselection procedures. In this case, the UE may manage the priority of the PLMN, based on the disaster roaming related information included in the reject message. For example, for a PLMN in which disaster roaming has occurred, control such as lowering the priority of the corresponding PLMN temporarily/for a specific time is included.

Alternatively, the UE may attempt another method for emergency call processing, such as performing a procedure for attempting an emergency call to the CS domain

The descriptions so far may be implemented in hardware. This will be explained.

<General Device to which the Disclosure of the Present Specification Can Be Applied>

Some of the disclosures of the present specification as described above are summarized as follows.

According to a disclosure of the present specification, a method in a network node for managing mobility in a second Public Land Mobile Network (PLMN) is provided. According to the method, an access request message for an access request from a User Equipment (UE) may be received through a base station in the second PLMN. And, a response message to the access request of the UE may be transmitted. Based on the UE being subscribed to a third PLMN and the base station transmitting system information including information on the first PLMN on behalf of a base station in the first PLMN, the response message may include information indicating rejection of the access request of the UE.

The response message may further include information indicating roaming to the second PLMN due to a failure occurring in the first PLMN.

The rejection indicated by the information may indicate a temporary rejection so that the UE can select the first PLMN again after a predetermined time after the access request of the UE is rejected.

The access request message may be received to the network node in the second PLMN through the base station in the second PLMN, instead of the first PLMN due to the failure of the first PLMN.

According to the method, after receiving the access request message from the UE, whether to accept or reject the access request of the UE may be determined. Based on determining to accept the access request of the UE, a range of a service may be further determined.

The determination of whether to accept or reject the access request of the UE may be performed based on whether the UE is subscribed to the third PLMN and whether the base station transmits system information including information on the first PLMN on behalf of the base station in the first PLMN.

For the determination, information may be obtained from an information server in the third PLMN to which the UE has subscribed.

The network node may be a Mobility Management Entity (MME), and the access request message may be an attach message.

Or, the network node may be an Access and mobility Management Function (AMF), and the access request message may be a registration request message.

Hereinafter, a device to which the above disclosure of the present specification can be applied will be described.

FIG. 17 illustrates a wireless communication system according to an embodiment.

Referring to FIG. 17 , the wireless communication system may include a first device 100 a and a second device 100 b.

The first device 100 a may be a base station, a network node, a transmission terminal, a reception terminal, a wireless device, a wireless communication device, a vehicle, a vehicle on which a self-driving function is mounted, a connected car, a drone (Unmanned Aerial Vehicle (UAV)), an Artificial Intelligence (AI) module, a robot, an Augmented Reality (AR) device, a Virtual Reality (VR) device, a Mixed Reality (MR) device, a hologram device, a public safety device, an MTC device, an Internet- of-Things (IoT) device, a medical device, a FinTech device (or financial device), a security device, a climate/environment device, a device related to 5G service or a device related to the fourth industrial revolution field.

The second device 100b may be a base station, a network node, a transmission terminal, a reception terminal, a wireless device, a wireless communication device, a vehicle, a vehicle on which a self-driving function is mounted, a connected car, a drone (Unmanned Aerial Vehicle (UAV)), an Artificial Intelligence (AI) module, a robot, an Augmented Reality (AR) device, a Virtual Reality (VR) device, a Mixed Reality (MR) device, a hologram device, a public safety device, an MTC device, an Internet-of-Things (IoT) device, a medical device, a FinTech device (or financial device), a security device, a climate/environment device, a device related to 5G service or a device related to the fourth industrial revolution field.

For example, the UE may include a cellular phone, a smart phone, a laptop computer, a terminal for digital broadcasting, a Personal Digital Assistants (PDA), a Portable Multimedia Player (PMP), a navigation, a slate PC, a tablet PC, an ultrabook, a wearable device (e.g., a watch type terminal (smartwatch), a glass type terminal (smart glass), a Head Mounted Display (HMD)), and so on. For example, the HMD may be a display device of a form, which is worn on the head. For example, the HMD may be used to implement VR, AR or MR.

For example, the drone may be a flight vehicle that flies by a wireless control signal without a person being on the flight vehicle. For example, the VR device may include a device implementing the object or background of a virtual world. For example, the AR device may include a device implementing the object or background of a virtual world by connecting it to the object or background of the real world. For example, the MR device may include a device implementing the object or background of a virtual world by merging it with the object or background of the real world. For example, the hologram device may include a device implementing a 360-degree stereographic image by recording and playing back stereographic information using the interference phenomenon of a light beam generated when two lasers called holography are met. For example, the public safety device may include a video relay device or an imaging device capable of being worn on a user's body. For example, the MTC device and the IoT device may be a device that does not require a person's direct intervention or manipulation. For example, the MTC device and the IoT device may include a smart meter, a vending machine, a thermometer, a smart bulb, a door lock or a variety of sensors. For example, the medical device may be a device used for the purpose of diagnosing, treating, reducing, handling or preventing a disease. For example, the medical device may be a device used for the purpose of diagnosing, treating, reducing or correcting an injury or obstacle. For example, the medical device may be a device used for the purpose of testing, substituting or modifying a structure or function. For example, the medical device may be a device used for the purpose of controlling pregnancy. For example, the medical device may include a device for medical treatment, a device for operation, a device for (external) diagnosis, a hearing aid or a device for a surgical procedure. For example, the security device may be a device installed to prevent a possible danger and to maintain safety. For example, the security device may be a camera, CCTV, a recorder or a blackbox. For example, the FinTech device may be a device capable of providing financial services, such as mobile payment. For example, the FinTech device may include a payment device or point of sales (POS). For example, the climate/environment device may include a device for monitoring or predicting the climate/environment.

The first device 100 a may include at least one processor such as a processor 1020 a, at least one memory such as memory 1010 a, and at least one transceiver such as a transceiver 1031 a. The processor 1020 a may perform the above-described functions, procedures, and/or methods. The processor 1020 a may perform one or more protocols. For example, the processor 1020 a may perform one or more layers of a radio interface protocol. The memory 1010 a is connected to the processor 1020 a, and may store various forms of information and/or instructions. The transceiver 1031 a is connected to the processor 1020 a, and may be controlled to transmit and receive radio signals.

The second device 100 b may include at least one processor such as a processor 1020 b, at least one memory device such as memory 1010 b, and at least one transceiver such as a transceiver 1031 b. The processor 1020 b may perform the above-described functions, procedures and/or methods. The processor 1020 b may implement one or more protocols. For example, the processor 1020 b may implement one or more layers of a radio interface protocol. The memory 1010 b is connected to the processor 1020 b, and may store various forms of information and/or instructions. The transceiver 1031 b is connected to the processor 1020 b and may be controlled transmit and receive radio signals.

The memory 1010 a and/or the memory 1010 b may be connected inside or outside the processor 1020 a and/or the processor 1020 b, respectively, and may be connected to another processor through various technologies, such as a wired or wireless connection.

The first device 100 a and/or the second device 100 b may have one or more antennas.

For example, an antenna 1036a and/or an antenna 1036b may be configured to transmit and receive radio signals.

FIG. 18 illustrates a block diagram of a network node according to an embodiment.

In particular, FIG. 18 is a diagram illustrating the network node of FIG. 17 in more detail when a base station is divided into a Central Unit (CU) and a Distributed Unit (DU).

Referring to FIG. 18 , base stations W20 and W30 may be connected to a core network W10. The base station W30 may be connected to a neighbor base station W20. For example, an interface between the base stations W20 and W30 and the core network W10 may be referred to as an NG. An interface between the base station W30 and the neighbor base station W20 may be referred to as an Xn.

The base station W30 may be divided into a CU W32 and DUs W34, W36. That is, the base station W30 may be hierarchically divided and operated. The CU W32 may be connected to one or more DUs W34, W36. For example, an interface between the CU W32 and the DU W34, W36 may be referred to as an Fl. The CU W32 may perform a function of higher layers of the base station. The DU W34, W36 may perform a function of lower layers of the base station. For example, the CU W32 may be a logical node that hosts Radio Resource Control (RRC), Service Data Adaptation Protocol (SDAP) and Packet Data Convergence Protocol (PDCP) layers of the base station (e.g., gNB). The DU W34, W36 may be a logical node that hosts Radio Link Control (RLC), Media Access Control (MAC) and physical (PHY) layers of the base station. Alternatively, the CU W32 may be a logical node that hosts RRC and PDCP layer of a base station (e.g., en-gNB).

An operation of the DU W34, W36 may be partially controlled by the CU W32. The one DU W34, W36 may support one or more cells. One cell may be supported by only the one DU W34, W36. The one DU W34, W36 may be connected to the one CU W32, and the one DU W34, W36 may be connected to a plurality of CUs by a proper implementation.

FIG. 19 is a block diagram of a UE according to an embodiment.

In particular, FIG. 19 is a diagram illustrating the UE of FIG. 17 in more detail above.

A UE includes a memory 1010, a processor 1020, a transceiver 1031, a power management module 1091, a battery 1092, a display 1041, an input unit 1053, a speaker 1042, a microphone 1052, a Subscriber Identification Module (SIM) card, and one or more antennas.

The processor 1020 may be configured to implement the proposed function, process and/or method described in the present specification. Layers of a wireless interface protocol may be implemented in the processor 1020. The processor 1020 may include Application-Specific Integrated Circuit (ASIC), other chipset, logical circuit and/or data processing apparatus. The processor 1020 may be an Application Processor (AP). The processor 1020 may include at least one of a Digital Signal Processor (DSP), a Central Processing Unit (CPU), a Graphics Processing Unit (GPU) and a modulator and demodulator (Modem). An example of the processor 1020 may be SNAPDRAGON™ series processor manufactured by Qualcomm®, EXYNOS™ series processor manufactured by Samsung®, A series processor manufactured by Apple®, HELIO™ series processor manufactured by MediaTek®, ATOM™ series processor manufactured by INTEL®, or the corresponding next generation processor.

The power management module 1091 manages a power for the processor 1020 and/or the transceiver 1031. The battery 1092 supplies power to the power management module 1091. The display 1041 outputs the result processed by the processor 1020. The input unit 1053 receives an input to be used by the processor 1020. The input unit 1053 may be displayed on the display 1041. The SIM card is an integrated circuit used to safely store International Mobile Subscriber Identity (IMSI) used for identifying a subscriber in a mobile telephoning apparatus such as a mobile phone and a computer and the related key. Many types of contact address information may be stored in the SIM card.

The memory 1010 is coupled with the processor 1020 in a way to operate and stores various types of information to operate the processor 1020. The memory may include Read-Only Memory (ROM), Random Access Memory (RAM), flash memory, a memory card, a storage medium, and/or other storage device. When the embodiment is implemented in software, the techniques described in the present specification may be implemented in a module (e.g., process, function, etc.) for performing the function described in the present specification. A module may be stored in the memory 1010 and executed by the processor 1020. The memory may be implemented inside of the processor 1020. Alternatively, the memory 1010 may be implemented outside of the processor 1020 and may be connected to the processor 1020 in communicative connection through various means which is well-known in the art.

The transceiver 1031 is connected to the processor 1020 in a way to operate and transmits and/or receives a radio signal. The transceiver 1031 includes a transmitter and a receiver. The transceiver 1031 may include a baseband circuit to process a radio frequency signal. The transceiver controls one or more antennas to transmit and/or receive a radio signal. In order to initiate a communication, the processor 1020 transfers command information to the transceiver 1031 to transmit a radio signal that configures a voice communication data. When receiving a radio signal, the transceiver 1031 may transfer a signal to be processed by the processor 1020 and transform a signal in baseband. The processed signal may be transformed into audible or readable information output through the speaker 1042.

The speaker 1042 outputs a sound related result processed by the processor 1020. The microphone 1052 receives a sound related input to be used by the processor 1020.

A user inputs command information like a phone number by pushing (or touching) a button of the input unit 1053 or a voice activation using the microphone 1052. The processor 1020 processes to perform a proper function such as receiving the command information, calling a call number, and the like. An operational data on driving may be extracted from the SIM card or the memory 1010. Furthermore, the processor 1020 may display the command information or driving information on the display 1041 such that a user identifies it or for convenience.

<Scenarios to Which the Disclosure of the Present Specification is Applicable>

Hereinafter, scenarios to which the present disclosure is applicable are described.

In the present specification, an always-on PDU session for URLLC having a low-latency characteristic may be used for artificial intelligence, robots, autonomous driving, extended reality, and the like among the 5G scenarios below.

FIG. 20 illustrates an example of 5G use scenarios.

The 5G usage scenarios illustrated in FIG. 20 are merely exemplary, and the technical features of the present specification may also be applied to other 5G usage scenarios that are not illustrated in FIG. 20 .

Referring to FIG. 20 , three major requirement areas of 5G include: (1) an enhanced Mobile Broadband (eMBB) area, (2) a massive Machine Type Communication (mMTC) area, and (3) an Ultra-Reliable and Low Latency Communications (URLLC) area. Some examples of usage may require multiple areas for optimization, while other examples of usage may focus only on one Key Performance Indicator (KPI). The 5G supports these various examples of usage in a flexible and reliable way.

The eMBB focuses generally on improvements in data rate, latency, user density, and capacity and coverage of mobile broadband access. The eMBB aims at a throughput of about 10 Gbps. The eMBB makes it possible to far surpass basic mobile Internet access, and covers full-duplex operations, media in cloud or augmented reality, and entertainment applications. Data is one of the key drivers of 5G, and it may not be possible to see dedicated voice services for the first time in the 5G era. In 5G, voice is expected to be processed as an application program simply using data connection provided by a communication system. A main reason for an increased traffic volume is an increase in content size and an increase in the number of applications requiring high data rates. Streaming services (audio and video), interactive video and mobile Internet connections will become more prevalent as more devices are connected to the Internet. Many of these applications require always-on connectivity to push real-time information and notifications to users. Cloud storage and applications are rapidly increasing in mobile communication platforms, which may be applied to both work and entertainment. Cloud storage is a special use case that drives the growth of uplink data rates. 5G is also used for remote work in the cloud and requires much lower end-to-end latency to maintain a good user experience when tactile interfaces are used. In entertainment, for example, cloud gaming and video streaming are another key factor requiring improvement in mobile broadband capabilities. Entertainment is essential on smartphones and tablets anywhere, including in highly mobile environments such as trains, cars and airplanes. Another use case is augmented reality and information retrieval for entertainment. Here, augmented reality requires very low latency and an instantaneous data amount.

The mMTC, which is designed to enable communication between a large number of low-cost devices powered by batteries, is provided to support smart metering, logistics, fields, and applications such as body sensors. The mMTC aims at about 10-year batteries and/or about one million devices per km². The mMTC enables seamless connection of embedded sensors in all fields to form a sensor network and is one of the most anticipated 5G use cases. Potentially, IoT devices are predicted to reach 20.4 billion by 2020. Smart networks utilizing industrial IoT is one of the areas where 5G plays a key role in enabling smart cities, asset tracking, smart utilities, agriculture and security infrastructure.

The URLLC, which enables devices and machines to communicate with high reliability, very low latency, and high availability, are ideal for vehicle communications, industrial control, factory automation, telesurgery, smart grid, and public safety applications. The URLLC aims at a delay of about 1 ms. The URLLC includes new services that will change the industry through ultra-reliable/low-latency links such as remote control of key infrastructures and autonomous vehicles. Levels of reliability and latency are essential for smart grid control, industrial automation, robotics, and drone control and adjustment.

Next, a plurality of usage examples included in the triangle of FIG. 20 will be described in more detail.

5G, which is a means of providing streams that are rated as hundreds of megabits per second to a gigabit per second, may complement Fiber-To-The-Home (FTTH) and cable-based broadband (or Data Over Cable Service Interface Specifications (DOCSIS)). Such a high speed may be required to deliver TVs with resolution of 4K or higher (6K, 8K and higher) as well as Virtual Reality (VR) and Augmented Reality (AR). VR and AR applications involve almost immersive sports events. Specific applications may require special network configuration. For example, in the case of VR games, a game company may need to integrate a core server with an edge network server of a network operator to minimize latency.

Automotive is expected to be an important new driver for 5G together with many use cases for mobile communication regarding vehicles. For example, entertainment for passengers require both high capacity and high mobile broadband. The reason is because future users will continue to expect high-quality connections, regardless of their location and speed. Another use case in the automotive sector is an augmented reality dashboard. The augmented reality dashboard allows drivers to identify objects in the dark on top of what they see through a front window. The augmented reality dashboard superimposes information to be provided to the driver regarding a distance and movement of objects. In the future, wireless modules will enable communication between vehicles, exchange of information between a vehicle and a supporting infrastructure, and exchange of information between a vehicle and other connected devices (e.g., devices carried by pedestrians). A safety system may lower the risk of accidents by guiding the driver to alternative courses of action to make driving safer. A next step will be a remotely controlled vehicle or an autonomous vehicle. This requires very reliable and very fast communication between different autonomous vehicles and/or between vehicles and infrastructure. In the future, autonomous vehicles will perform all driving activities and drivers will be forced to focus only on traffic anomalies that the vehicle itself cannot identify. The technical requirements of autonomous vehicles require ultra-low latency and ultra-fast reliability to increase traffic safety to levels that cannot be achieved by humans.

Smart cities and smart homes referred to as smart society will be embedded with high-density wireless sensor networks as an example of smart networks. A distributed network of intelligent sensors will identify the conditions for cost and energy efficient maintenance of a city or home. A similar setup may be done for each household. Temperature sensors, window and heating controllers, burglar alarms, and home appliances are all wirelessly connected. Many of these sensors typically require low data rates, low power, and low cost. However, for example, real-time HD video may be required in certain types of devices for surveillance.

The consumption and distribution of energy including heat or gas is highly decentralized, requiring automated control of distributed sensor networks. A smart grid interconnects these sensors using digital information and communication technologies to collect information and act accordingly. This information may include the behavior of suppliers and consumers, so that the smart grid may improve efficiency, reliability, economical efficiency, sustainability of production, and a distribution of fuels such as electricity in an automated manner. The smart grid may also be considered as another low-latency sensor network.

A health sector has many applications that may benefit from mobile communications. The communication system may support telemedicine providing clinical care from remote locations. This may help reduce barriers to distance and improve access to medical services that are not consistently available in remote rural areas. It is also used to save lives in critical care and emergencies. A wireless sensor network based on mobile communication may provide remote monitoring and sensors for parameters such as a heart rate and blood pressure.

Wireless and mobile communications are becoming increasingly important in industrial applications. Wiring is expensive to install and maintain. Thus, a possibility of replacing cables with reconfigurable wireless links is an attractive opportunity for many industries. However, achieving this requires that a wireless connection operates with a delay, reliability and capacity similar to those of a cable and requires simplified management. Low latency and very low error probability are new requirements that need to be connected to 5G.

Logistics and cargo tracking is an important use case for mobile communications that enables tracking of inventory and packages from anywhere using a location-based information system. Logistics and freight tracking use cases typically require low data rates but require a wide range and reliable location information.

<Artificial Intelligence (AI)>

Artificial intelligence refers to a field of studying artificial intelligence or a methodology for creating the same, and machine learning refers to a field of defining various problems dealing in an artificial intelligence field and studying methodologies for solving the same. The machine learning may be defined as an algorithm for improving performance with respect to a certain task through repeated experiences with respect to the task.

An Artificial Neural Network (ANN) is a model used in machine learning. It can mean a whole model of problem-solving ability, consisting of artificial neurons (nodes) that form a network of synapses. An ANN can be defined by a connection pattern between neurons in different layers, a learning process for updating model parameters, and/or an activation function for generating an output value.

The ANN may include an input layer, an output layer, and optionally one or more hidden layers. Each layer includes one or more neurons, and the ANN may include neurons and synapses connecting neurons. In the ANN, each neuron may output a function value of an activation function for input signals input through a synapse, a weight, and a bias.

A model parameter means a parameter determined through learning, and includes the weight of the synaptic connection and the bias of the neuron. In addition, the hyperparameter refers to a parameter that should be set before learning in a machine learning algorithm, and includes a learning rate, the number of iterations, a mini- batch size, an initialization function, etc.

The purpose of learning the ANN can be seen as determining the model parameters that minimize the loss function. The loss function may be used as an index for determining optimal model parameters in the learning process of the ANN.

Machine learning can be classified into supervised learning, unsupervised learning, and reinforcement learning according to a learning method.

Supervised learning may refer to a method of training the ANN in a state where a label for training data. The label may refer a correct answer (or result value) that the ANN should infer when training data is input to the ANN. Unsupervised learning may refer to a method of training the ANN in a state where no labels are given for training data. Reinforcement learning may refer to a learning method in which an agent defined in a certain environment learns to select an action or sequence of actions that maximizes the cumulative reward in each state.

Among ANNs, machine learning implemented as a Deep Neural Network (DNN) including a plurality of hidden layers is also called deep learning, and deep learning is a part of machine learning. Hereinafter, machine learning is used in a sense including deep learning.

<Robot>

A robot may refer to a machine which automatically handles a given task by its own ability, or which operates autonomously. Particularly, a robot that functions to recognize an environment and perform an operation according to its own judgment may be referred to as an intelligent robot.

Robots may be classified into, for example, industrial, medical, household, and military robots, according to the purpose or field of use.

A robot may include an actuator or a driving unit including a motor in order to perform various physical operations, such as moving joints of the robot. In addition, a movable robot may include, for example, a wheel, a brake, and a propeller in the driving unit thereof, and through the driving unit, may thus be capable of traveling on the ground or flying in the air.

<Self-Driving or Autonomous-Driving>

Autonomous driving refers to self-driving technology, and an autonomous vehicle refers to a vehicle that moves without any manipulation by a user or with minimum manipulation by a user.

For example, autonomous driving may include all of a technology for keeping a vehicle within a driving lane, a technology for automatically controlling a speed such as an adaptive cruise control, a technology for automatically driving the vehicle along a determined route, and a technology for, when a destination is set, automatically setting a route and driving the vehicle along the route.

A vehicle includes a vehicle having only an internal combustion engine, a hybrid vehicle having both an internal combustion engine and an electric motor, and an electric vehicle having only an electric motor, and may include not only an automobile but also a train, a motorcycle, or the like.

In this case, an autonomous vehicle may be considered as a robot with an autonomous driving function.

<Extended Reality; XR>

Extended reality collectively refers to Virtual Reality (VR), Augmented Reality (AR), and Mixed Reality (MR). The VR technology provides real world objects or backgrounds only in CG images, the AR technology provides virtual CG images together with real object images, and the MR technology is computer graphic technology for mixing and combining virtual objects with the real world.

The MR technology is similar to the AR technology in that both real and virtual objects are shown together. However, there is a difference in that a virtual object is used to complement a real object in the AR technology, whereas a virtual object and a real object are used in an equivalent nature in the MR technology.

The XR technology may be applied to a Head-Mount Display (HMD), a Head-Up Display (HUD), a mobile phone, a tablet PC, a laptop, a desktop, a TV, digital signage, etc. A device to which the XR technology is applied may be referred to as an XR device.

FIG. 21 shows an AI system 1 according to an embodiment.

Referring to FIG. 21 , an AI system 1 is connected to at least one of an AI server 200, a robot 100 a, a self-driving vehicle 100 b, an XR device 100 c, a smartphone 100 d, or home appliances 100 e over a cloud network 10. In this case, the robot 100 a, the self-driving vehicle 100 b, the XR device 100 c, the smartphone 100 d or the home appliances 100 e to which the AI technology has been applied may be called AI devices 100 a to 100 e.

The cloud network 10 may be a network that constitutes a part of a cloud computing infrastructure or a network that exists in the cloud computing infrastructure. Here, the cloud network 10 may be configured using a 3G network, a 4G or LTE network, or a 5G network.

The devices 100 a to 100 e and 200 configuring the AI system 1 may be interconnected over the cloud network. Particularly, the devices 100 a to 100 e and 200 may communicate with each other through a base station but may directly communicate with each other without the intervention of a base station.

The AI server 200 may include a server that performs AI processing and a server that performs an operation on big data.

The AI server 200 is connected to at least one of the robot 100 a, the self-driving vehicle 100 b, the XR device 100 c, the smartphone 100 d or the home appliances 100 e, that is, AI devices configuring the AI system, over the cloud network 10 and may help at least some of the AI processing of the connected AI devices 100 a to 100 e.

In this case, the AI server 200 may train an artificial neural network based on a machine learning algorithm in place of the AI devices 100 a to 100 e, may directly store a learning model or may transmit the learning model to the AI devices 100 a to 100 e.

In this case, the AI server 200 may receive input data from the AI devices 100 a to 100 e, may deduce a result value of the received input data using the learning model, may generate a response or control command based on the deduced result value, and may transmit the response or control command to the AI devices 100 a to 100 e.

Alternatively, the AI devices 100 a to 100 e may directly deduce a result value of input data using a learning model and may generate a response or control command based on the deduced result value.

Hereinafter, various embodiments of the AI devices 100 a to 100 e to which the aforementioned technology is applied will be described.

<AI+Robot>

The robot 100 a, which adopts an AI technology, may be implemented as a guide robot, a transport robot, a cleaning robot, a wearable robot, an entertainment robot, a pet robot, an unmanned flying robot, and the like.

The robot 100 a may include a robot control module for controlling an operation, and the robot control module may refer to a software module or a chip implemented with hardware.

The robot 100 a may acquire status information of the robot 100 a using sensor information acquired from various types of sensors, detect (recognize) surrounding environments and objects, generate map data, determine moving routes and driving plans, determine responses to user interactions, or determine actions.

Here, the robot 100 a may use sensor information obtained from at least one sensor from among LIDAR, radar, and camera to determine a moving route and a driving plan.

The robot 100 a may perform the above operations using a learning model including at least one artificial neural network. For example, the robot 100 a may recognize a surrounding environment and an object using a learning model and may determine an operation using the recognized surrounding environment information or object information. Here, the learning model may be directly learned by the robot 100 a or learned by an external device such as the AI server 200.

Here, the robot 100 a may directly generate a result using a learning model and perform an operation, or transmit sensor information to an external device such as the AI server 200, receive a result generated accordingly, and perform an operation.

The robot 100 a may determine a moving path and a driving plan using at least one of map data, object information detected from sensor information, or object information acquired from an external device, and control a driving unit to drive the robot 100 a according to the moving path and the driving plan.

The map data may include object identification information on various objects arranged in a space in which the robot 100 a moves. For example, the map data may include object identification information on fixed objects such as walls and doors and movable objects such as flower pots and desks. In addition, the object identification information may include a name, a type, a distance, and a location.

In addition, the robot 100 a may perform an operation or run by controlling the driving unit based on the user's control/interaction. In this case, the robot 100 a may acquire interaction intention information according to a user's motion or voice speech, determine a response based on the acquired intention information, and perform an operation.

<AI+Autonomous-Driving/Self-Driving>

The autonomous vehicle 100 b may be implemented as a mobile robot, a vehicle, an unmanned aerial vehicle, etc., to which AI technology is applied.

The autonomous vehicle 100 b may include an autonomous driving control module for controlling the autonomous driving function, and the autonomous driving control module may refer to a software module and/or a chip implementing the software module. The autonomous driving control module may be included in the autonomous vehicle 100 b as a component of the autonomous vehicle 100 b, but may be connected to the outside of the autonomous vehicle 100 b with separate hardware.

The autonomous vehicle 100 b may acquire the state information of the autonomous vehicle 100 b using the sensor information acquired from various kinds of sensors and/or detect (recognize) the surrounding environment and/or the object, and/or generate map data, and/or determine a travel route and/or a travel plan, and/or determine an operation.

Like the robot 100 a, the autonomous vehicle 100 b can use the sensor information acquired from at least one sensor among the LIDAR, the radar, and/or the camera to determine the travel route and/or the travel plan.

In particular, the autonomous vehicle 100 b can recognize an environment and/or an object for an area in which the field of view is obscured and/or over a certain distance by receiving sensor information from external devices, and/or receive the recognized information directly from external devices.

The autonomous vehicle 100 b can perform the above-described operations using a learning model composed of at least one ANN. For example, the autonomous vehicle 100 b can recognize the surrounding environment and/or the object using the learning model, and can determine the travel route using the recognized surrounding information and/or the object information. The learning model may be learned directly from the autonomous vehicle 100 b and/or learned from an external device such as the AI server 200.

In this case, the autonomous vehicle 100 b may perform an operation by generating a result using a direct learning model, but the autonomous vehicle may also perform operation by transmitting sensor information to an external device such as the AI server 200 and receiving the generated result.

The autonomous vehicle 100 b may determine the travel route and/or the travel plan using at least one of the map data, the object information detected from the sensor information and/or the object information acquired from the external device, and drive the autonomous vehicle 100 b according to the determined travel route and/or travel plan by controlling the driving unit.

The map data may include object identification information on various objects arranged in a space (e.g. road) in which the autonomous vehicle 100 b moves. For example, the map data may include object identification information on fixed objects such as street lamps, rocks, and buildings, and/or on movable objects such as vehicles and pedestrians. The object identification information may include a name, a type, a distance, and/or a position, etc.

Also, the autonomous vehicle 100 b may perform the operation and/or run by controlling the driving unit based on the control/interaction of the user. The autonomous vehicle 100 b may acquire the intention information of the interaction due to the user's operation and/or voice utterance, determine the response based on the acquired intention information, and perform the operation.

<AI+XR>

The XR device 100 c may be implemented as a HMD, a HUD, a TV, a mobile phone, a smartphone, a computer, a wearable device, a home appliance, a digital signage, a vehicle, a fixed robot, a mobile robot, etc., to which AI technology is applied.

The XR device 100 c analyzes the three-dimensional point cloud data and/or image data acquired from various sensors and/or from an external device to generate position data and/or attribute data for the three-dimensional points, thereby obtaining information about the surrounding space and/or the real object, and outputting the rendered XR object. For example, the XR device 100 c may output an XR object, which includes the additional information about the recognized object, by corresponding to the recognized object.

The XR device 100 c can perform the above-described operations using a learning model composed of at least one ANN. For example, the XR device 100 c can recognize a real object from three-dimensional point cloud data and/or image data using the learning model, and can provide information corresponding to the recognized real object. The learning model may be learned directly from the XR device 100 c and/or learned from an external device such as the AI server 1200.

In this case, the XR device 100 c may perform an operation by generating a result using a direct learning model, but the autonomous vehicle may also perform operation by transmitting sensor information to an external device such as the AI server 200 and receiving the generated result.

<AI+Robot+Autonomous-Driving/Self-Driving>

The robot 100 a may be implemented as a guide robot, a carrying robot, a cleaning robot, a wearable robot, an entertainment robot, a pet robot, an unmanned flying robot, etc., to which AI technology and autonomous-driving technology are applied.

The robot 100 a, to which the AI technology and the autonomous-driving technology are applied, may mean the robot 100 a having the autonomous-driving function itself and/or the robot 100 a interacting with the autonomous vehicle 100 b.

The robot 100 a having an autonomous-driving function can collectively refer to devices that move by themselves in accordance with a given travel route and/or move by determining the traveling route by themselves without user's control.

The robot 100 a having the autonomous-driving function and the autonomous vehicle 100 b can use a common sensing method to determine at least one of the travel route and/or the travel plan. For example, the robot 100 a having the autonomous-driving function and the autonomous vehicle 100 b can determine at least one of the travel route and/or the travel plan using the information sensed through the LIDAR, the radar, and/or the camera.

The robot 100 a interacting with the autonomous vehicle 100 b may exist separately from the autonomous vehicle 100 b, and the robot 100 a interacting with the autonomous vehicle 100 b may be associated with the autonomous-driving function inside and/or outside the autonomous vehicle 100, and/or may perform an operation associated with the user aboard the autonomous vehicle 100 b.

The robot 100 a interacting with the autonomous vehicle 100 b may acquire the sensor information on behalf of the autonomous vehicle 100 b and provide it to the autonomous vehicle 100 b, or the robot 100 a interacting with the autonomous vehicle 100 b may obtain the sensor information and generate the environment information and/or the object information to provide the autonomous vehicle 100 b, thereby controlling and/or assisting the autonomous-driving function of the autonomous vehicle 100 b.

Or, the robot 100 a interacting with the autonomous vehicle 100 b may monitor the user boarding the autonomous vehicle 100 b and/or may control the functions of the autonomous vehicle 100 b through interaction with the user. For example, when it is determined that the driver is in a drowsy state, the robot 100 a may activate the autonomous-driving function of the autonomous vehicle 100 b and/or assist the control of the driving unit of the autonomous vehicle 100 b. The function of the autonomous vehicle 100 b controlled by the robot 100 a may include not only an autonomous-driving function but also a function provided by a navigation system and/or an audio system provided in the autonomous vehicle 100 b.

Or, the robot 100 a interacting with the autonomous vehicle 100 b may provide information and/or assist the function to the autonomous vehicle 100 b outside the autonomous vehicle 100 b. For example, the robot 100 a, such as a smart traffic light, may provide traffic information including signal information, etc., to the autonomous vehicle 100 b. The robot 100 a, such as an automatic electric charger of an electric vehicle, may interact with the autonomous vehicle 100 b to connect the electric charger to the charging hole automatically.

<AI+Robot+XR>

The robot 100 a may be implemented as a guide robot, a carrying robot, a cleaning robot, a wearable robot, an entertainment robot, a pet robot, an unmanned flying robot, a drone, etc., to which AI technology and XR technology are applied.

The robot 100 a to which the XR technology is applied may refer to a robot that is subject to control/interaction in the XR image. In this case, the robot 100 a may be separated from the XR device 100 c and can be associated with each other.

When the robot 100 a that is the subject to control/interaction in the XR image acquires the sensor information from the sensors including the camera, the robot 100 a and/or the XR device 100 c may generate an XR image based on the sensor information and the XR device 100 c can output the generated XR image. The robot 100 a can operate based on a control signal and/or a user's interaction input through the XR device 100 c.

For example, the user can acknowledge the XR image corresponding to the viewpoint of the robot 100 a remotely linked through the external device such as the XR device 100 c, and can adjust the autonomous travel path of the robot 100 a, control operation and/or driving, or check the information of neighboring objects, through interaction.

<AI+Autonomous-Driving/Self-Driving+XR>

The autonomous vehicle 100 b may be implemented as a mobile robot, a vehicle, an unmanned aerial vehicle, etc., to which AI technology and XR technology are applied.

The autonomous driving vehicle 100 b to which the XR technology is applied may mean an autonomous vehicle having means for providing an XR image and/or an autonomous vehicle that is subject to control/interaction in the XR image. Particularly, the autonomous vehicle 100 b that is subject to control/interaction in the XR image may be separated from the XR device 100 c and can be associated with each other.

The autonomous vehicle 100 b having the means for providing the XR image can acquire the sensor information from the sensors including the camera and output the generated XR image based on the acquired sensor information. For example, the autonomous vehicle 100 b may include an HUD to output an XR image, thereby providing a passenger with a real object and/or an XR object corresponding to an object in the screen.

At this time, when the XR object is output to the HUD, at least a part of the XR object may be output so as to overlap with the actual object that the passenger's gaze is directed to. On the other hand, when the XR object is output to the display provided in the autonomous vehicle 100 b, at least a part of the XR object may be output so as to overlap with the object in the screen. For example, the autonomous vehicle 100 b can output XR objects corresponding to objects such as a lane, another vehicle, a traffic light, a traffic sign, a two-wheeled vehicle, a pedestrian, a building, etc.

When the autonomous vehicle 100 b that is the subject to control/interaction in the XR image acquires the sensor information from the sensors including the camera, the autonomous vehicle 100 b and/or the XR device 100 c may generate an XR image based on the sensor information and the XR device 100 c can output the generated XR image. The autonomous vehicle 100 b can operate based on a control signal and/or a user's interaction input through the XR device 100 c.

In the above, preferred embodiments have been exemplarily described, but the disclosure of the present specification is not limited to such specific embodiments, and thus, it may be modified, changed, or improved in various forms within the scope set forth in the claims. 

1. A method for a User Equipment (UE) subscribed to a first Public Land Mobile Network (PLMN) to perform access, the method comprising: transmitting a first request message to a network node via a base station, wherein the base station is a base station of a second PLMN that broadcasts system information including information of the first PLMN; receiving a first response message for the first request message from the network node, wherein the first response message includes information informing that there is a service failure in the first PLMN; and transmitting a second request message to the second PLMN or performing a procedure of reselecting another PLMN, instead of the first PLMN having the service failure, based on the first response message including the information.
 2. The method of claim 1, wherein the first response message is an attach accept message or an attach reject message, based on the first request message being an attach request message, wherein the first response message is a registration accept message or a registration reject message, based on the first request message being a registration request message.
 3. The method of claim 1, wherein the procedure of reselecting another PLMN is performed, based on the first request message being a registration request message and the first response message being a registration reject message.
 4. The method of claim 1, wherein the transmitting the second request message to the second PLMN is performed, based on the first request message being a registration request message and the first response message being a registration accept message, and wherein the second request message is a session establishment request message.
 5. The method of claim 4, wherein the method further comprises receiving a second response message for the second request message, and wherein the second response message includes a session establishment accept message or a session establishment reject message, based on the second request message being a session establishment request message.
 6. The method of claim 5, wherein the session establishment reject message includes information informing that there is a service failure in the first PLMN.
 7. The method of claim 5, wherein the method further comprises performing a deregistration procedure or a procedure of reselecting another PLMN, based on receiving the session establishment reject message including informing that there is a service failure in the first PLMN.
 8. The method of claim 5, wherein the method further comprises transmitting a Session Initiation Protocol (SIP)-based request message to an IP Multimedia Subsystem (IMS) node, based on receiving the session establishment accept message, which is the second response message.
 9. A User Equipment (UE) subscribed to a first Public Land Mobile Network (PLMN), the UE comprising: a transceiver; and a processor configured to control the transceiver, wherein the processor is configured to control the transceiver to transmit a first request message to a network node via a base station, wherein the base station is a base station of a second PLMN that broadcasts system information including information of the first PLMN, wherein the processor is configured to control the transceiver to receive a first response message for the first request message from the network node, wherein the first response message includes information informing that there is a service failure in the first PLMN, and wherein the processor is configured to transmit a second request message to the second PLMN or perform a procedure of reselecting another PLMN, instead of the first PLMN having the service failure, based on the first response message including the information.
 10. The UE of claim 9, wherein the first response message is an attach accept message or an attach reject message, based on the first request message being an attach request message, wherein the first response message is a registration accept message or a registration reject message, based on the first request message being a registration request message.
 11. The UE of claim 9, wherein the processor is configured to perform the procedure of reselecting another PLMN, based on the first request message being a registration request message and the first response message being a registration reject message.
 12. The UE of claim 9, wherein the processor is configured to transmit the second request message to the second PLMN, based on the first request message being a registration request message and the first response message being a registration accept message, and wherein the second request message is a session establishment request message.
 13. The UE of claim 12, wherein the processor is configured to receive a second response message for the second request message, and wherein the second response message includes a session establishment accept message or a session establishment reject message, based on the second request message being a session establishment request message.
 14. The UE of claim 13, wherein the session establishment reject message includes information informing that there is a service failure in the first PLMN. 